There is considerable interest in the commercial development of coal liquification processes to produce fuels which are convenient to handle. Liquified coal must meet certain specifications regarding mineral (ash and sulfur) content for use as boiler and gas turbine fuels. In general, liquified coals include asphaltic materials (asphaltenes and pre-asphaltenes) together with such mineral matter, typically including silicates and iron sulfides as major components.
The coal-derived asphaltic materials have lower molecular weight than asphaltenes from petroleum origin and strongly influence the viscosity of the liquified coal. It is thought that anti-solvent precipitation of such asphaltic materials causes the concommitant precipitation of such mineral matter. The initial rate of precipitation from asphaltics, and thus removal of mineral matter, is known to be increased by the addition of anti-solvent which decrease the solubilities of the asphaltic materials. A wide variety of hydrocarbons are known to be useful anti-solvents for this purpose.